Understanding the physiological properties of odontoblasts is an important step towards understanding the cellular mechanisms that account for metabolic and transductive processes in dental pulp. Indirect evidence now suggests that such processes are mediated by alterations in transmembrane conductances via ion channels in the odontoblast membrane. Among the most critical of these ionic pathways are those that govern calcium turnover. Calcium regulation is especially important for odontoblast cells, since both intra- and extracellular calcium levels may fluctuate during dentinogenesis, and these cells may be directly involved in transporting calcium to the mineralizing matrix. In addition to mineralogenesis, odontoblast ion channels may also be involved in somatosensation, mediating changes in hydrostatic pressure and/or changes in the osmotic gradient produced by mechanical or hydrodynamic perturbation. The primary objective of the proposed research is to examine the ionic mechanisms underlying the response of these cells to factors associated with dentinogenesis and somatosensory transduction in dental pulp. In these studies I will use patch-clamp recording techniques to monitor single- channel and whole-cell current in the odontoblast membrane using both in vitro and in situ preparations of intact mammalian odontoblast cells. In preliminary studies I have identified an L-type calcium channel as well as a cation-conducting mechanosensitive ("stretch-activated") channel in these cells. The proposed studies will be directed towards a quantitative analysis of these and other conductances, and will include an examination of the effects of dentinotrophic, neurogenic, and inflammatory factors linked to physiological or pathophysiological responses in dental pulp. In preliminary studies l have also identified neural-like non-odontoblast satellite cells in explant-derived pulp cell cultures. Specifically, cultured pulp cells contained a voltage-gated sodium conductance with kinetic properties similar to those of glial or Schwann cells, neuronal satellite cells found in both the peripheral and central nervous systems. In addition, pulp cells were reactive to antibodies that typically label regenerating cells in the nervous system, as well as developing pulp cells in teeth. Thus, these cultures may represent a model for injury, recovery, and/or maturation of non-odontoblast cells in dental pulp. In the nervous system, it has been suggested that such satellite cells may contribute to sensitization of adjacent primary afferents, by alterations in the density, distribution or kinetic properties of it's sodium current. Thus, a second objective of the proposed research is to determine whether the pulp cell sodium current may have a similar functional role in dental pulp, by monitoring its physiological and kinetic properties, and the distribution and density of the underlying sodium channels during maturation of pulp cell cultures. In these experiments, cultures will be treated with agents known to induce differentiation, e.g., growth factors, dexamethasone, or DMSO, and patch-clamp recordings made in parallel with immunohistochemical studies using a monoclonal antibody to the sodium channel itself.